全文获取类型
收费全文 | 5197篇 |
免费 | 163篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 184篇 |
大气科学 | 650篇 |
地球物理 | 1206篇 |
地质学 | 2038篇 |
海洋学 | 259篇 |
天文学 | 808篇 |
综合类 | 15篇 |
自然地理 | 219篇 |
出版年
2021年 | 68篇 |
2020年 | 71篇 |
2019年 | 59篇 |
2018年 | 137篇 |
2017年 | 148篇 |
2016年 | 231篇 |
2015年 | 143篇 |
2014年 | 212篇 |
2013年 | 276篇 |
2012年 | 131篇 |
2011年 | 194篇 |
2010年 | 204篇 |
2009年 | 261篇 |
2008年 | 172篇 |
2007年 | 167篇 |
2006年 | 151篇 |
2005年 | 130篇 |
2004年 | 109篇 |
2003年 | 104篇 |
2002年 | 126篇 |
2001年 | 103篇 |
2000年 | 87篇 |
1999年 | 94篇 |
1998年 | 95篇 |
1997年 | 83篇 |
1996年 | 70篇 |
1995年 | 76篇 |
1994年 | 92篇 |
1993年 | 46篇 |
1992年 | 45篇 |
1991年 | 52篇 |
1990年 | 58篇 |
1989年 | 50篇 |
1988年 | 42篇 |
1987年 | 50篇 |
1986年 | 38篇 |
1985年 | 55篇 |
1984年 | 58篇 |
1983年 | 67篇 |
1982年 | 55篇 |
1981年 | 53篇 |
1980年 | 45篇 |
1979年 | 39篇 |
1978年 | 69篇 |
1977年 | 37篇 |
1976年 | 42篇 |
1975年 | 50篇 |
1974年 | 58篇 |
1973年 | 61篇 |
1962年 | 30篇 |
排序方式: 共有5379条查询结果,搜索用时 31 毫秒
1.
Himmerfjärd is a Swedish estuary bordering on the Baltic. The estuary lacks astronomical tides and its circulation is driven by winds and freshwater runoff. Because of a tertiary sewage treatment plant located at its inner end, the estuary is becoming increasingly eutrophic. A field study was carried out for a 78-day period in late summer and early fall of 1977 to determine rates of nutrient transport and to construct nutrient budgets. Since physical parameters (current velocity, temperature, salinity, winds and water level changes) were measured more frequently than nutrients (phosphate, nitrate, nitrite and ammonium) it was necessary to develop a suitable method to calculate nutrient flux time series and net nutrient fluxes. Over the study period, Himmerfjärd imported phosphorus and exported nitrogen. Direction of nutrient fluxes and changes in flux direction were consistent with the structure of the baroclinic currents. 相似文献
2.
3.
Gösta Gahm 《Astrophysics and Space Science》2006,304(1-4):149-152
The number of confirmed and suspected close T Tauri binaries (period days) is increasing. We discuss some systems with enhanced emission line activity and periodic line profile changes. Non-axisymmetric flows of plasma in the region between the circumbinary disk and the stars can be generated through the influence of the secondary component. Such enhanced activity is found around binaries with eccentric as well as circular orbits. We discuss our observations of the T Tauri stars RW Aurigae A and RU Lupi, which may host very close brown dwarf companions. Model simulations indicate that non-axisymmetric flows are generated around close binaries with circumbinary disks, also in systems with circular orbits. 相似文献
4.
Joachim Köppen 《Astrophysics and Space Science》2003,284(2):837-840
Representative results from a comparison of the chemical evolution of spherical collapse models without and with a intercloud
medium are presented. The hot metal-rich gas distributes quickly the metals produced in supernovae throughout the galaxy,
thus leading to a more homogeneous chemical evolution and flatter metallicity gradients in the gas and the stars. The stellar
population is somewhat less concentrated towards the centre. The strong outflow results in a substantial loss of metals from
the galaxy to its surroundings, and a lower effective yield in the galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
We present warm dark matter (WDM) as a possible solution to the missing satellites and angular momentum problem in galaxy
formation and introduce improved initial conditions for numerical simulations of WDM models, which avoid the formation of
unphysical haloes found in earlier simulations. There is a hint, that because of that the mass function of satellite haloes
has been overestimated so far, pointing to higher values for the WDM particle mass.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Summary ?The rare earth, major and trace element geochemistry of Jurassic deep marine manganese shales allow insight into their environment
of deposition. We present data of 24 samples from the Northern Calcareous Alps (Eastern Alps), collected from Late Jurassic
strata of the Tennengebirge and from Early Jurassic strata of the Karwendel Mts. Whereas major and trace element geochemistry
is controlled by the detrital input, rare earth element data and the relationship between total organic carbon and (pyritic)
sulfur can be used to constrain the origin of the manganese accumulation. The data of this study are compatible with a hydrogenous
precipitation of manganese by strongly varying redox-conditions at the sediment–water interface of a slope basin.
Received December 21, 2001; revised version accepted February 18, 2002 相似文献
7.
Radiative Transfer (RT) codes with image capability are a fundamental tool for preparing interferometric observations and
for interpreting visibility data. In view of the upcoming VLTI facilities, we present the first comparison of images/visibilities
coming from two 3D codes that use completely different techniques to solve the problem of self-consistent continuum RT. In
addition, we focus on the astrophysical case of a disk distorted by tidal interaction with by-passing stars or internal planets
and investigate for which parameters the distortion can be best detected in the mid-infrared using the mid-infrared interferometric
device MIDI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Judit Györgyey 《Celestial Mechanics and Dynamical Astronomy》1985,36(3):281-285
The non-linear stability of motions around L5 in the elliptic restricted problem of the three bodies is investigated numerically with emphasis on the effect of the orbital eccentricity of the primaries on the shape of the established stability regions. It is shown that with increasing eccentricity, the width of these regions is decreasing. 相似文献
9.
We study the temporal intensity variations of Mgib bright features and investigate the corresponding Hα velocity pattern.
The network bright features are well visible in the continuum, in images averaged over the duration of the observations (130 min).
We detected `flashing' bright features, which appear and disappear within two to five minutes, while the rest of the bright
features undergo small variations of either their shape and/or their intensity. A power spectrum analysis reveals a 10-min
oscillation for approximately half of the stable bright features. The 5-min oscillations are detected mainly at the network
boundaries, where stable bright features are located, while 3-min oscillations coincide with few bright features, but are
also quite intense inside the network cells. The majority of bright features are associated with Hα downflows. The downflow
is very intense at the location of `flashing' bright features. 相似文献
10.